DCP I is a newly characterized yeast phosphatase that is believed to play a role in the removal of the 5' 7-methyl-Guanine cap of mRNA to allow for efficient mRNA degradation. Structural and biochemical studies are being undertaken on this enzyme. MALDI-MS is used to map limited digests of the protein to elucidate the folding domains of the protein and determine useful constructs for growing protein crystals sufficient for high resolution X-ray crystallographic studies.